Beginning college students may be unclear about the types of materials that they can refer to in papers, so it is necessary to provide an overview of different types of sources, and why some are preferred, possibly acceptable, or not suitable for college papers (e.g., research papers and essays). These generally fall into the category of general, popular sources, which are usually not suitable for college papers (but with exceptions), and academic papers. However, some better quality, higher level non-academic sources are typically used, especially for first-year (and second-year) papers. These will be referred to as professional sources here.

• Academic sources: Written by academic experts on the topic, for others in their academic, scholarly, or research community, or at least for those with some academic knowledge of the field.
• Professional sources: Written by academic experts or otherwise trained professionals, and written for educated non-experts.
• Popular or general sources: Written probably by non-experts on the topic, for a general audience.

See also: Academic versus non-academic writing

Sources can be categorized as academic, professional, or popular by the following criteria.

1. Author (including qualifications, credentials, expertise)
2. Audience
3. Information (type, quality, and depth of information; primary or secondary information)
4. Quality control (mechanisms to ensure the information is accurate and of good quality)

These in turn affect factors like tone, style, and the type of venue where it is published.

For more on these types of sources, see the following pages on the English Wiki. 

1. Academic versus non-academic sources
2. Popular sources
3. Unreliable sources
4. Professional sources
5. Academic sources

See alo the following pages on the English Wiki Youtube channel.

1. Evaluating sources #1: Introduction
2. Evaluating sources #2: Popular sources